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Thin Cylinders.

First Case^ Thin Cylinders, — A boiler, or thin cylinder abed.
Fig. 351, tends to tear along the joints a b and cd. Examining a
strip i ''wide we obtain:

Internal load on
projected area

I — / sa^e strengtrl OI"two sections of
)      \          plate (in tension).

; x 2 rx i =ft x 2/x i.

/.   ptonsr = f ft

Suppose the plate tends to tear at a ring section as at <?/, then.
/tons x TT rz = /t x 2 TT r x t.

From this we find that


Stress on longitudinal section = —
and stress on transverse section = \ —

so there is no fear of a boiler bursting at a cross seam. The
above supposes the boiler plate to be of uniform construction
throughout. But as the seams, whether welded or riveted, are
much weaker than the * solid ' plate, a multiplier (?/) must be in-
troduced on the right side of the equation to reduce the quantity
and shew the strength at the joint. Then :

strength of joint
strength of solid plate
efficiency per cent = ğ7 x 100

) = efficiency =


For lap welded joints,
For single riveted joints,
For double riveted joints, 77 =


________________ jm^ tj      .* >roughly

For electric welded joints, 77 = -85 )     (See p. 755.)
and the formula for boilenor pipe strength becomes

Example 6.— A copper steam pipe 12" dia. is to resist ağ internal
pressure of 160 Ibs. per sq. in. Find its thickness, if ^ for the brazed
joint = 80%

From above formula    - - x 6 == 2 x /x *8        .*.   / ğ '267 ins.
2240                     „           - •